This invention relates to a process for preparation of lubricating oil stocks. In particular, it relates to a specific combination of unit processes whereby a hydrocarbonaceous feedstock is hydrocracked and subsequently dewaxed using a specific crystalline silicoaluminophosphate catalyst. The lube oil stocks so produced have a relatively low pour point, and excellent viscosity and viscosity index (VI) properties.
High-quality lubricating oils are critical for the machinery of modern society. Unfortunately, the supply of natural crude oils having good lubricating properties, e.g., Pennsylvania and Arabian Light feedstocks, is not enough to meet the demand. Additionally, because of uncertainties in world crude oil supplies, it is necessary to be able to produce high-quality lubricating oils efficiently from ordinary crude feedstocks.
Numerous processes have been proposed to produce lubricating oils by upgrading the ordinary and low-quality stocks which ordinarily would be converted into other products.
The desirability of upgrading a crude fraction normally considered unsuitable for lubricant manufacture into one from which good yields of lubes can be obtained has long been recognized. Hydrocracking processes have been proposed to accomplish such upgrading. U.S. Pat. Nos. 3,506,565, 3,637,483 and 3,790,472 teach hydrocracking processes for producing lubricating oils.
Hydrocracked lubricating oils generally have an unacceptably high pour point and require dewaxing. Solvent dewaxing is a well-known and effective process but expensive. More recently, catalytic methods for dewaxing have been proposed. U.S. Pat. No. Re. 28,398 discloses dewaxing petroleum charge stocks using ZSM-5 type zeolites. U.S. Pat. No. 3,755,145 discloses a process for preparing low pour point lube oils by hydrocracking a lube oil stock using a catalyst mixture comprising a conventional cracking catalyst and ZSM-5.
It has also been suggested that in order to improve the oxidation resistance of lubricants it is often necessary to hydrogenate or hydrofinish the oil after hydrocracking, with and without catalytic dewaxing as illustrated in U.S. Pat. Nos. 4,325,805; 4,347,121; 4,162,962; 3,530,061; and 3,852,207. U.S. Pat. Nos. 4,283,272 and 4,414,097 teach continuous processes for producing dewaxed lubricating oil base stocks including hydrocracking a hydrocarbon feedstock, catalytically dewaxing the hydrocrackate and hydrofinishing the dewaxed hydrocrackate. These patents teach the use of catalysts comprising zeolite ZSM-5 and ZSM-23 respectively for the dewaxing phase.
All the foregoing patents indicate the state of the hydrocracking, dewaxing and stabilization art and are incorporated herein by reference as background.
A problem with the prior art processes for producing high-quality lubricating oils is the fact that the dewaxing processes used therein, such as when using dewaxing catalyst ZSM-5, function by means of cracking reactions, and therefore a number of useful products become degraded to lower molecular weight materials. For example, waxy paraffins may be cracked down to butane, propane, ethane and methane and so may the lighter n-paraffins which do not, in any event, contribute to the waxy nature of the oil. Because these lighter products are generally of lower value than the higher molecular weight materials, it would obviously be desirable to limit the degree of cracking which takes place during the catalytic dewaxing process. Also, the products obtained by the process of this invention have better viscosities and viscosity indexes at a given pour point as compared to the prior art processes using alumino-silicate zeolites such as ZSM-5.